1. Field of the Invention
The present invention relates to electronic imaging systems and, more particularly, to a high resolution CMOS imaging system especially suitable for use in a periscope head that yields a continuous 360-degree field-of-view without mechanical rotation.
2. Description of Prior Art
A periscope “head” is the top portion of a periscope that contains the lenses and mirrors used to observe what is outside certain vehicles, including submarines, armored cars, spacecraft and their rovers.
Conventional periscope systems employ a full length sealed outer casing with an interior rotatable mast, and various observation optics and sensors mounted on the mast. While theses optics used to be lenses, many modern periscopes employ electronic imagers such as charge-coupled devices (CCDs). For example, U.S. Pat. No. 6,347,010 to Chen et al. issued Feb. 12, 2002 shows a a periscope with an IR sensor, visible CCD camera, and a laser range finder.
The instantaneous horizontal field of view (FOV) is defined as the field of view obtained at a single fixed observation point, allowing for rotation of the eye about this point but not the translation of the eye's position. Because periscopes contain an entrance and exit aperture separated optically by some distance, they form an apparent tunnel through which the observer sees. When the instantaneous field of view of a single periscope is limited by the entrance aperture, one or both side walls of the tunnel will be seen by the observer. This is generally the case with conventional periscopes because their exit and entrance apertures are substantially the same size.
Thus, current US Navy periscope sensor heads utilizes CCD technology with a variable X-magnification field-of-view sensor.
Wide-angle coverage has been attempted by arranging a plurality of periscopes side-by-side along an arc. However, since each periscope has a limited field of view and one or both side walls of each periscope will always be visible, these visible side walls will act as visual blockages.
Additionally, whenever multiple imagers are employed the amount of data complicates the issue. Search and detection require wide field-of-view (FOV), tracking requires fast frame-rate data output from regions of interest (ROI), target recognition requires high spatial resolution, and multi-target cueing requires all four of the foregoing. The use of an optical zoom is one way, but an extremely inefficient way of carrying out these diverse tasks because it cannot simultaneously provide narrow and wide field of view scene visualization. It is often difficult for an operator to quickly zoom in and out of the ROI because of the vast changes in the FOV during zooming and relocating contacts within the search FOV (which may be 50× higher magnification).
It would be greatly advantageous to provide an improved high resolution CMOS imaging system especially suitable for use in a periscope head that yields a continuous 360-degree field-of-view without mechanical rotation with electronically selectable, low and high-resolution fields-of-view environment. The foregoing would be well suited for use in a variety of vehicles, and particularly in extraterrestrial rovers (such as the Mars Science Laboratory (MSL) rover under development.